Babies all grow at their own speed, but most follow a basic pattern. A baby generally doubles her birth weight by around age 5 months, Mayo Clinic pediatrician Jay L. Hoecker explains, and triples it at 1 year. Very large newborns or premature babies might not conform to the norms, however. Your doctor will track your newborn's growth and address any deviation from normal weight gain.
Typical Weight Gain
Most babies gain between 5 and 7 ounces per week in the first six months of life, or between 1.25 and 2 pounds per month, according to Hoecker. For an 8-pound infant, a gain of 2 pounds per month would mean he'd reach 16 pounds by around age 4 months. A 10-pound newborn, on the other hand, would take 5 months to double his birth weight if he gained 2 pounds per month.
Exceptions to the Rules
Premature babies may double their birth weight at different rates than average-sized babies. Premature babies often develop complications that can slow weight gain; special charts for preemies are a better way to track their progress. Once they're well, preterm babies often make up for lost time in weight gain. A 1993 study published in the Journal of Tropical Pediatrics found that preterm babies weighing between 1,000 and 1,500 grams, or between slightly more than 2 to 3 pounds, who were exclusively breastfed after discharge from the special care nursery, doubled their birth weight at age 10 weeks. Babies who weighed between around 3 to 4.5 pounds doubled their birth weight by 12 weeks.
Breast Vs. Bottle Weight Gain
Around age 4 months, breastfed and bottle-fed babies start to gain weight at slightly different rates. Bottle-fed babies gain weight more quickly, while breastfed babies are leaner -- although both groups have similar growth in length and head circumference. During the first year of life, breastfed babies gain an average of 1 pound less than formula-fed babies, notes AskDrSears.com. Because weight charts are designed with formula-fed infants in mind, your baby might appear to be falling below her expected weight gain, but this is normal for breastfed infants. The World Health Organization has revised its infant weight charts to reflect this.
Causes for Variations
Babies who double their birth weight too slowly could have failure-to-thrive syndrome and might need their food intake adjusted. Babies who double their birth weight too quickly might be victims of overfeeding. It's easier for parents to encourage a baby to finish up the last few ounces in a bottle than it is to keep a breastfed baby nursing once he's full. Breastfeeding may protect against obesity because breastfed babies learn to self-regulate their food intake. Talk to your doctor if your baby seems to gain weight too fast or doesn't gain fast enough.